Some critics have said such measures are extreme and won't prevent a terrorist from getting the same information elsewhere.

'A lot of this stuff is kind of feel-good measures without thinking about: Will this really work?' said Gabriel Goldberg, president of Computers and Publishing Inc. of Alexandria, Va. 'All it does it slow things down and, even worse, it gives the illusion of security.'

Agency webmasters aren't the only ones taking information off their sites. Some major corporations also have decided to err on the side of caution, McClellan said.

The Office of Pipeline Safety, a division of the Transportation Department, pulled the National Pipeline Mapping System off its site. The geographic information systems database contains information on the location and other attributes of natural gas and hazardous liquid pipelines across the country. It also shows heavily populated and sensitive areas as well as maps of drinking water systems, according to a DOT spokesman.

'I don't know when or if they'll be putting it back up,' the spokesman said.

A federal overreaction?

The office will continue to provide data to pipeline operators, as well as to federal, state and local government officials.

Meanwhile, several watchdog groups have criticized the rush to alter federal Web sites and have accused the government of overreacting.

OMB Watch, a nonprofit group, has posted a list, at www.ombwatch.org, of some of the items removed from government sites at the federal and state levels.

Goldberg said he is not opposed to the government removing information that could pose a risk.

'There does seem to be a downside to dangerous information being made too easily available,' he said. 'My biggest question is, [who will] strike the right balance between what people are able to post and who is able to do the controlling?'

Goldberg said he is worried that security controls could grow into political tools. 'Having the government control what's available on the Web seems a very, very dangerous path to go down,' he said.

'Right now there's no good answer. Once you start censoring, you've lost what America is fighting for'and, for two, it's futile' because the information being taken from the Web might already have been copied.

In late September, the National Imagery and Mapping Agency began blocking public access to some of its maps of military installations as well as topographic maps of the United States, NIMA spokesman John Iler said.

At that time the agency, which conducts mapping and imaging for the Defense Department, also instructed the Library of Congress and the National Archives and Records Administration to deny public access to the maps.

But that lasted only a few days, Iler said, so agency employees could review the documents. NIMA has since put the maps back up for public use.

The National Guard took a map off its site that linked users to its state offices. Mark Allen, a spokesman for the Guard, said the decision to suspend the link was made to give state chapters a chance to review their information to see if it contained sensitive data.

The Federal Energy Regulatory Commission has removed documents that contain details about energy facilities. A note posted on the commission's site says the move was prompted by the attacks.

The Nuclear Regulatory Commission removed most of its site, including detailed technical data on nuclear reactors, after the attacks. It left an explanation of what the agency does, news releases, public meeting notices, and employment and contracting opportunities. The NRC said late last week it will phase in a new site in the next several weeks.